The role of GABA, catecholamine and endorphins in the response of hypothalamus to different psychoactive drugs was studied by monitoring eating behavior, pituitary hormone release and pituitary cAMP content. Eating behavior is under GABA, catecholamine and endorphin control. It appears that GABA neurons are distal to noradrenergic and endorphin containing neurons since blockade of GABA receptors inhibits eating induced by all three receptor agonist. Prolactin release is regulated by hypothalamic DA and endorphin but not by GABA receptors. The control of prolactin release by GABA occurs at the pituitary level. Pituitary cAMP is under independent DA, GABA and enkephalin control. Changes of cAMP content induced by these transmitter receptor agonist or antagonists are associated with release of ACTH.